How to test SMTP server on Linux?
To check if SMTP is working from the command line (Linux), is one critical aspect to be considered while setting up an email server. The most common way of checking SMTP from Command Line is using telnet, openssl or ncat (nc) command. It is also the most prominent way to test SMTP Relay.
How to check mail service in Linux?
Type "ps -e | grep sendmail" (without quotes) at the command line. Press the "Enter" key. This command prints a listing that includes all running programs whose name contains the text "sendmail." If sendmail is not running, there will be no results.